Automatic rollover marine turbine control

ABSTRACT

An automatic rollover circuit is included in a marine turbine control system, the automatic rollover circuit capable of detecting zero-shaft speed and directing an output signal to the valve position control for opening either ahead and astern valves. If rollover is detected, then the automatic rollover circuit is reset to await the next zero-speed condition. If rollover does not occur, the automatic rollover circuit is reset to attempt a rollover in the opposite direction and a shaftstopped alarm is activated. A rollover trip circuit is also included as a protective device when the automatic rollover circuit is in use.

United States Patent Cronin et al. Oct. 14, 1975 [54] AUTOMATIC ROLLOVER MARINE 3,817,651 6/1974 Law at al. 415/30 X TURBINE CONTROL [75] lnventors: Michael J. Cronin, Salem; Bruce D. 53;7 2 32 ri g igg g f Taber Box both of Mass Attorney, Agent, or Firm-John F. Ahern; James W. [73] Assignee: General Electric Company, Mitchell Schenectady, NY.

[22] Filed: Apr. 12, 1974 [57] ABSTRACT [21] A l, N 460,369 An automatic rollover circuit is included in a marine turbine control system, the automatic rollover circuit capable of detecting zero-shaft speed and directing an E 60/706; g output signal to the valve position control for opening either ahead and astem valves. lf rollover is detected, [58] Fleld of Search 9 then the automatic rollover circuit is reset to await the 60/646 0 415/13 36 next zero-speed condition. If rollover does not occur,

the automatic rollover circuit is reset to attempt a roll- [56] References C'ted over in the opposite direction and a shaft-stopped UNITED STATES PATENTS alarm is activated. A rollover trip circuit is also in-' 2.847,6|7 12/1958 Clark, Jr. 60/700 X eluded as a protective device when the automatic roll- 3,l50,549 9/1964 60/701 X over circuit is in use. 3,36l,l08 l/l968 60/646 X 3,643,437 2 1972 Birnbaum et al. 60/646 10 Clalms, 5 Drawlng Figures SHAFT STOPPED ALARM VALVE POSITION sET COMMAND AUTOMATIC r JQQE EQ 'IQL E EL Bk L E LL g g l ,5 & STEAM N A c HYDRAULIC i gggggg; 2 RATE 3%.??? mama TOR T SSE VALVING VALVES I l POSITION FEEDBACK .SPEED FEED BA CK CLHQUIT F W THROTTLE SPEED I CONTROL 2 SPEED SIGNAL I: l

INPUT REFERENCE B l HPS US. Patent Oct. 14, 1975 Sheet 3 of3 3,911,685

5150 mm 2955MB Q P312- 44266 Qmmmm H mmEC. m

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429m oummm AUTOMATIC ROLLOVER MARINE TURBINE CONTROL BACKGROUND OF THE INVENTION This invention relates generally to turbine control systems; and, in particular, this invention is applicable to marine steam turbine control systems.

During startup and shutdown of a marine steam turbine there is a danger that the turbine rotor may become distorted if allowed to cool or heat up nonuniformly. To prevent this thermal distortion, the shaft must be rotated at low speeds until sufficiently heated or cooled. This may be done by turning gear or by manual actuation of the steam valve control whenever the shaft speed approaches zero-speed. Zero-shaft speed may be defined as less than one-half shaft revolution per minute.

While the foregoing procedures may be adequate to prevent shaft distortion, the turning gear solution has a disadvantage because of the time it takes to convert from turning gear operation to steam operation. This delay could be critical in the case of modern super tankers which may be required to leave an offshore unloading area quickly under the threat of fire. In the instance of manual operation, the required observation is tedious and subject to operator error.

It is one object of the present invention to provide a turbine control system which provides automatic shaft rollover upon detection of zero-speed condition.

It is another object of the present invention to provide an automatic turbine control system which will alternately reverse the shaft rollover direction until rollover is achieved.

It is another object of the present invention to provide a turbine control system which will signal a shaftstopped alarm, if the shaft cannot be rolled; but which will continue attempts to roll the shaft in alternate directions until the system is disabled.

It is still another object of the present invention to provide circuit malfunction protection in the automatic rollover mode.

In accordance with the aforementioned objects, a marine turbine control system is provided with an automatic rollover circuit including a shaft speed input and a valve position set command output. The input shaft speed signal is watched by a zero-speed detection circuit and a rollover detection circuit connected in parallel. If a zero-speed condition is detected, a delayed signal activates a valve position set circuit which provides a valve position set command to the turbine valve position control circuit. An ahead/astern logic circuit controls the polarity of the valve position set command so that the turbine is alternately rolled in the ahead or astern direction. If the rollover attempt fails, the zerospeed detection circuit and valve position set circuit is reset by a valve open timer and another attempt to roll the turbine is made in an opposite direction. Meanwhile a shaft-stopped alarm is sounded. If the rollover is successful, the zero-speed detection circuit, the valve position set circuit, and valve open timer are reset by the rollover detection circuit to await the next zerospeed condition. A rollover trip circuit is also enabled by a signal from the valve position set circuit.

The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof, may best be understood with reference to the following description, taken in connection with the appended drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a marine turbine control system from throttle to turbine incorporating the automatic rollover circuit according to the present invention.

FIG. 2 is a schematic diagram of the automatic rollover circuit including a shaft speed input and a valve position set command output.

FIG. 3 is a schematic diagram of the zero-speed detection circuit and valve set delay timer.

FIG. 4 is a schematic diagram of one embodiment of a timer device useful in the present invention.

FIG. 5 is a diagrammatic representation of the rollover detection circuit.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, the throttle control is set to produce both a valve position reference signal and a speed reference signal. In summing junction A, the valve position reference is added to the actual valve position (feedback) to provide a valve position error signal. In summing junction B, the speed reference signal is added with the actual speed signal to provide a speed error signal. In summing junction C, the valve position error signal and the speed error signal are added to provide a valve position command which reflects both the valve position error signal and the speed error signal. During normal operations, the automatic rollover circuit is disabled and hence its output signal (valve position set command) is zero. The valve position command (summation of the valve position error and speed error) is input into a fourth summing junction D which determines flow from a variable displacement pump used for actuating the turbine valves. The operation of the variable displacement pump in conjunction with actuating the turbine valves is the subject of U.S. patent application Ser. No. 410.929 for a Valve Actuating System filed Oct. 29, 1973 for'Taber and Cronin, assigned to the assignee of the present invention.

Referring to FIG. 2, an automatic rollover control circuit is shown in more detail. Redundant pickup speed signals HPSl and HPS2 are provided from the high-pressure turbine shaft by means of a toothed wheel and magnetic pickup. The speed signals are in the form of digital pulse trains whose repetition rate is proportional to turbine speed. The redundant speed signals are input into an Automatic Switching Input Check Circuit which produces a single speed signal output. The Automatic Switching Input Check Circuit uses HPSl as the primary control signal, but if this should fail, it disables HPSl as an input and automatically switches to HPS2 as the control signal.

The Automatic Switching Input Check Circuit output I speed signal is input to a Zero-Speed Detection Circuit and Rollover Detection Circuit, both of which are in parallel. The Zero-Speed Detection Circuit is an asynchronous digital circuit which enables a Valve Set Delay Timer if there is a zero-speed detection. Zerospeed is defined as a shaft speed of less that one-half revolution per minute. The Valve Set Delay Timer has an adjustable delay setting which is usually set for a 1- minute delay. At the end of the l-minute delay, a signal from the timer activates a Valve Position Set Circuit which has been preset to the amount of valve opening in the turbine control valves. The output signal of the Valve Position Set Circuit is further modified by an Ahead-Astem Direction Control (a flip-flop device) which then either causes the ahead or the astern turbine valves to open in the amount preset in the Valve Position Set Circuit. Hence, returning to FIG. 1, it is seen that a speed input signal, to the Automatic Rollover Circuit, which is identified as a zero-speed signal results in an output signal from the Automatic Rollover Circuit which is a valve position set command. The valve position set command is a reference input to the valve position control circuit and hence sets the turbine valves.

Returning to FIG. 2, if rollover is accomplished, it is sensed by a Rollover Detection Circuit. The Rollover Detection Circuit is set so that it is activated by the digital pulse train speed signal input where the pulse interval is greater than one-half shaft revolution per minute. Activation of the Rollover Detection Circuit resets the Zero-Speed Detection Circuit and the Valve Position Set Circuit. Thereafter, the next zero-speed condition is awaited.

The Valve Position Set Circuit also activates a Valve Open Timer which is a delay timer with a nominal delay of one minute. If a zero-speed condition is sensed and thereafter the turbine shaft is rolled, the Valve Open Timer is reset by the Rollover Detection Circuit. If there is no rollover, the timer activates a shaft-stopped alarm and resets the Zero-Speed Detection Circuit and the Valve Position Set Circuit so that rollover is then attempted in the opposite direction.

The Valve Position Set Circuit also resets the Valve Set Delay Timer and enables a Rollover Trip Circuit.

The Rollover Trip Circuit includes a digital speed signal input LPSl taken from the low-pressure turbine. If the speed signal indicates a turbine speed of greater than 15% of rated turbine speed, then a signal output from the Rollover Trip Circuit (Malfunction Trip) is gated with the valve position control circuit output to assure that the 15% speed signal is due to an Automatic Rollover Circuit Malfunction and not any other control mode. The trip is hydraulic and is known in the prior art. Additionally, this trip is interlocked with the throttle control which must be set at zero to operate the Automatic Rollover Control Circuit.

Referring now to FIG. 3, in conjunction with the aforementioned FIGS. 1 and 2, the zero-speed detection circuit is a combination of a retriggerable monostable multivibrator P1 and flip-flop circuits employing NAND gates. The retriggerable monostable multivibrator may be of the type known as a Fairchild 9601 having a fixed timed output signal set by an RC time constant (T). The speed signal input is a digital pulse train whose repetition rate is proportional to shaft speed. If the repetition rate of the speed pulses exceeds T, then the output of 1 will be high. If the repetition rate of the speed signal falls below T, then the output of P1 goes low and sets FFl (flip-flop). The T constant of P1 corresponds to the time delay between arriving speed pulses representing a shaft speed of one-half RPM.

Flip-flop circuit FFl is made up of two, two input NAND gates (Fairchild 9949). A set or reset command is a logic low signal. A logic low input to S will cause the 1 output to be high and the output to be low. A low input to R will cause the 1 output to be low and the 0 output to be high. Operation is asynchronous.

After FFl is set, its output signal 1 is gated in a NAND gate with the 0 output of FFZ. This is an interlock which means that the circuits must be in the reset mode (the 1 output low, the 0 output high) for proper operation. This insures that once a valve set command has been initiated it will not be disrupted by the zerospeed detection circuit. This is important when the shaft is forced to zero and rotated in the opposite direction.

The signal will now set the timer which until this time is being held in reset by using a NAND gate as a logical inverter from the set signal to the reset line. This insures that the set reset operation of the timer control is mutually exclusive. The timer represents the valve set delay timer. When it times itself out, it emits a high pulse that is logically inverted by another NAND gate to set FF2 and the I output thereof sets the valve position set circuit. Another zero-speed condition can only be detected after both FH and FF2 have been reset. The reset signal will come either from the Rollover Detection Circuit or the Valve Open Timer.

Referring to FIG. 4, an example of a timer device is shown. When the timer is in the reset mode a switch connects the 741 operational amplifier (connected as an integrator) inverting input to a negative reference voltage through an input resistor. The 741 operational amplifier is held in positive saturation, about 12 V, DC. The comparator C is set to trigger on a negative voltage.

The timer is started by switching the 741 input to a positive reference voltage (adjustable by means of a potentiometer). The 741 amplifier then starts to integrate negatively as a function of R, C, and the voltage at the slider of P When this voltage reaches the set point of comparator C, set by potentiometer P the comparator fires and a logic compatible signal is output. The time delay is controlled by the reference voltage at P and the comparator set point, determined by P To reset the timer the switch position is reversed and the 741 amplifier will have a negative reference voltage. The reset mode is faster than the timer mode by making the time constant R C much smaller than time constant R C Also the negative reference voltage is much greater. The analog switches are controlled by a flip-flop. A set signal to the flip-flop closes S and opens 8,, thereby starting the timer. A reset signal to the flip-flop closes S, and open S FIG. 5 is a diagrammatic representation of the rollover detection circuit. Two retriggerable monostable multivibrators P and P have different time constants T and T wherein T is greater than T P is used as a delay device whereas P is the primary detection device. The digital speed signal triggers P and as long as the time delay between arriving speed pulses is greater than T of P P will have pulsed outputs. The 0 output of P is used to trigger P Two NAND gates in series are used to delay the 1 output of P before it is gated with the 0 output of P The NAND gates in series compensate for the propagation delay incurred when triggering P When the time between arriving speed pulses is less than T; of P (T is set such that it is equal to the time between speed pulses that would correspond to a shaft speed slightly greater than one-half RPM), the output of P 1 stays high. P is no longer being triggered and times itself out and its 0 output will go high. The P 1 output is gated with the P 0 output (both high) providing a rollover detection signal.

The rollover trip circuit is similar to the aforementioned rollover detection circuit and therefore would be obvious to one of ordinary skill in the art. to derive the rollover trip circuit from the teachings of FIG. 5 and the foregoing explanation.

The operation of the Automatic Rollover Circuit is as follows. When the throttle control is set to zero, it is still desirable to keep the shaft rotating to prevent distortion of the shaft. This is the function of the Automatic Rollover Circuit which provides a valve position set command when a zero-speed condition is detected. The valve position set command is introduced into the valve position control circuit shown in FIG. 1 and operates the turbine control valves. Again, it is emphasized that during the operation of the Automatic Rollover Circuit, the throttle is set at zero and an interlock between the Automatic Rollover Circuit and the throttle control is provided for this purpose.

Redundant high-pressure turbine speed signals are introduced into the Automatic Rollover Circuit into an asynchronous switching circuit which can detect failure of one of the input signals and which then can utilize the working signal for control. The input speed signal is ignored allowing the turbine to coast until such time as a zero-speed condition exists. This condition is detected by a Zero-Speed Detection Circuit (an asynchronous digital circuit which looks at the time interval between speed pulses) which activates a Valve Position Set Circuit after a nominal delay set by the Valve Set Delay Timer. The Valve Position Set Circuit and the Ahead/Astem Direction Control direct the Marine Turbine Control to open either the Ahead or Astern valves and sets the amount (position) of the valve opening. Simultaneously, with this signal to the turbine control, the Valve Set Delay Timer is reset; the Valve Open Timer is Set and the Rollover Trip Circuit is set. lf the turbine shaft is rolled, this is detected by the Rollover Detection Circuit which resets the Zero-Speed Detection Circuit; resets (closes) the Valve Position Set Circuit and resets the Valve Open Timer. The turbine shaft then coasts until the next zero-speed condition is detected.

If within the 1-minute delay of the Valve Open Timer, the shaft does not roll, a signal from the timer activates a shaft-stopped alarm and resets the Zero- Speed Detection Circuit and Valve Position Set Circuit. Thereafter the zero-speed is again detected and a valve position set command is activated for turning the shaft in the other direction. If, in the course of Automatic Rollover Circuit control, the turbine speed exceeds 15% of rated speed (as detected from an alternate turbine speed pickup) then a signal (malfunction trip) is gated with the valve position control output signal to shut down the turbine.

While there is shown what is considered, at present, to be the preferred embodiment of the invention, it is, of course, understood that various other modifications may be made therein. It is intended to claim all such modifications as fall within the true spirit and scope of the present invention.

What is claimed is:

1. In a turbine control system including a valve position control circuit for controlling the flow of a motive bine shaft zero-speed condition, the automatic rollover circuit comprising:

a. at least one shaft speed signal input;

b. means responsive to the shaft speed signal input for detecting a zero-speed condition of the turbine shaft;

0. a valve position set circuit for providing a valve position set command signal in response to a signal from the zero-speed detection means; and,

d. means responsive to the shaft speed signal input for detecting turbine shaft rollover; the rollover detection means output signal providing a reset signal to the zero-speed detection means and the valve position set circuit upon detection of turbine shaft rollover.

2. The automatic rollover circuit recited in claim 1 wherein the zero-speed detection means and the shaft rollover detection means are connected in parallel and are responsive to the shaft speed signal input.

3. The automatic rollover circuit recited in claim 1 wherein the shaft speed input signal is a digital pulse train whose repetition rate is proportional to shaft speed; and, wherein the zero-speed detection means includes a retriggerable monostable multivibrator having a time constant corresponding to a digital pulse train repetition rate of approximately one-half shaft revolution per minute.

4. The automatic rollover circuit recited in claim 1 wherein the shaft speed input signal is a digital pulse train whose repetition rate is proportional to shaft speed; and, wherein the rollover detection means includes at least one retriggerable monostable multivibrator having a time constant corresponding to a digital pulse train repetition rate slightly greater than one-half shaft revolution per minute.

5. The automatic rollover circuit recited in claim 1 further comprising:

a. a first signal delay means between the zero-speed detection means output and the valve position set circuit input, the first signal delay means being reset by the valve position set circuit output; and,

b. a second signal delay means set by the valve position set circuit for resetting the zero-speed detection means and valve position set circuit, the second signal delay means reset by a signal from the rollover detection means.

6. The automatic rollover circuit recited in claim 1 further including a rollover trip circuit, the rollover trip circuit enabled by a signal from the valve position set circuit; and, the rollover trip circuit further comprising:

a. a second shaft speed signal input comprising a digital pulse train whose repetition rate is proportional to shaft speed; and,

b. at least one retriggerable monostable multivibrator receiving the second shaft speed signal input, the retriggerable monostable multivibrator having a time constant corresponding to a digital pulse train repetition rate of a selected percent of turbine rated speed.

7. The automatic rollover circuit recited in claim 6 wherein the rollover trip circuit output signal is gated with the valve position control circuit output signal.

8. The automatic rollover circuit recited in claim 1 further including means for directing the valve position set command signal alternately in an ahead and astern direction, the means interposed between the valve position set circuit and the valve position control circuit.

9. In a turbine control system including a valve position control circuit for controlling the flow of motive fluid to at least one turbine; an automatic rollover circuit for providing a valve position set command signal to the valve position control circuit in response to a turbine shaft zero-speed condition, the automatic rollover circuit comprising:

a. at least one shaft speed signal input;

b. means responsive to the shaft speed signal input for detecting a zero-speed condition of the turbine shaft;

c. a valve position set circuit for providing a valve position set command signal in response to a signal from the zero-speed detection means;

d. means responsive to the shaft speed signal input for detecting turbine shaft rollover; the zero-speed detection means and rollover detection means connected in parallel with the shaft speed signal input;

and, the rollover detection means output signal providing a first reset signal to the zero-speed detection means and the valve position set circuit upon detection of turbine shaft rollover;

e. a first signal delay means between the zero-speed detection means output and the valve position set circuit input, the first signal delay means being reset by the valve position set circuit output; and,

f. a second signal delay means set by the valve posiwherein the zero-speed detection means and the rollover detection means are asynchronous digital circuits 

1. In a turbine control system including a valve position control circuit for controlling the flow of a motive fluid to at least one turbine; an automatic rollover circuit for providing a valve position set command signal to the valve position control circuit in response to a turbine shaft zero-speed condition, the automatic rollover circuit comprising: a. at least one shaft speed signal input; b. means responsive to the shaft speed signal input for detecting a zero-speed condition of the turbine shaft; c. a valve position set circuit for providing a valve position set command signal in response to a signal from the zero-speed detection means; and, d. means responsive to the shaft speed signal input for detecting turbine shaft rollover; the rollover detection means output signal providing a reset signal to the zero-speed detection means and the valve position set circuit upOn detection of turbine shaft rollover.
 2. The automatic rollover circuit recited in claim 1 wherein the zero-speed detection means and the shaft rollover detection means are connected in parallel and are responsive to the shaft speed signal input.
 3. The automatic rollover circuit recited in claim 1 wherein the shaft speed input signal is a digital pulse train whose repetition rate is proportional to shaft speed; and, wherein the zero-speed detection means includes a retriggerable monostable multivibrator having a time constant corresponding to a digital pulse train repetition rate of approximately one-half shaft revolution per minute.
 4. The automatic rollover circuit recited in claim 1 wherein the shaft speed input signal is a digital pulse train whose repetition rate is proportional to shaft speed; and, wherein the rollover detection means includes at least one retriggerable monostable multivibrator having a time constant corresponding to a digital pulse train repetition rate slightly greater than one-half shaft revolution per minute.
 5. The automatic rollover circuit recited in claim 1 further comprising: a. a first signal delay means between the zero-speed detection means output and the valve position set circuit input, the first signal delay means being reset by the valve position set circuit output; and, b. a second signal delay means set by the valve position set circuit for resetting the zero-speed detection means and valve position set circuit, the second signal delay means reset by a signal from the rollover detection means.
 6. The automatic rollover circuit recited in claim 1 further including a rollover trip circuit, the rollover trip circuit enabled by a signal from the valve position set circuit; and, the rollover trip circuit further comprising: a. a second shaft speed signal input comprising a digital pulse train whose repetition rate is proportional to shaft speed; and, b. at least one retriggerable monostable multivibrator receiving the second shaft speed signal input, the retriggerable monostable multivibrator having a time constant corresponding to a digital pulse train repetition rate of a selected percent of turbine rated speed.
 7. The automatic rollover circuit recited in claim 6 wherein the rollover trip circuit output signal is gated with the valve position control circuit output signal.
 8. The automatic rollover circuit recited in claim 1 further including means for directing the valve position set command signal alternately in an ahead and astern direction, the means interposed between the valve position set circuit and the valve position control circuit.
 9. In a turbine control system including a valve position control circuit for controlling the flow of motive fluid to at least one turbine; an automatic rollover circuit for providing a valve position set command signal to the valve position control circuit in response to a turbine shaft zero-speed condition, the automatic rollover circuit comprising: a. at least one shaft speed signal input; b. means responsive to the shaft speed signal input for detecting a zero-speed condition of the turbine shaft; c. a valve position set circuit for providing a valve position set command signal in response to a signal from the zero-speed detection means; d. means responsive to the shaft speed signal input for detecting turbine shaft rollover; the zero-speed detection means and rollover detection means connected in parallel with the shaft speed signal input; and, the rollover detection means output signal providing a first reset signal to the zero-speed detection means and the valve position set circuit upon detection of turbine shaft rollover; e. a first signal delay means between the zero-speed detection means output and the valve position set circuit input, the first signal delay means being reset by the valve position set circuit output; and, f. a second signal delay means set by the valve position set circuit for providing a second reset signal to the zero-speed detection means and valve position set circuit, the second signal delay means reset by a signal from the rollover detection means.
 10. The automatic rollover circuit recited in claim 9 wherein the zero-speed detection means and the rollover detection means are asynchronous digital circuits. 